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Predict whether the following is neutral, basic, or acidic and the pH

  1. Jul 26, 2014 #1
    1. 0.250 M of NH4Br



    2. Ka for NH4 = 5.52 x 10-10 and Kb for NH3 = 1.81 x 10-5


    3. So I broke the salt down into its constituents and considering Br is neutral and NH4 is an acid, NH4Br is acidic. I am just confused with how to calculate the pH. I thought that I should do this....NH4 + H2O → NH3 + H3)
    At equilibrium, NH4 = (0.1 M -x) NH3 = +x and H3O = +x
    Then the Ka value 5.52 x 10-10 = x2/(0.25-x) and then solve for x

    The x value = the concentration of H3) and then I take the -log(H3O).

    I keep getting the wrong answer, so I am just wondering if the steps I have taken are correct? Also, the pH = 4.92
     
    Last edited: Jul 26, 2014
  2. jcsd
  3. Jul 26, 2014 #2
    I actually just the got answer. But if someone could reply in regards to why the pH of the salt solution of o,25 M NH4Br = the dissociation of NH4 to give H3O?
     
  4. Jul 27, 2014 #3
    HBr is a strong acid. As such, the Br will not react with H2O to form HBr. Thus, the pH is completely dependent on the Ka of NH4, which determines the concentration of H3O+ in solution.
     
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